The invention concerns the physical design of an adaptive hearing protective earplug combined with an audio communications terminal
There exist a lot of solutions for hearing protection and audio communication in noisy environments based on earplugs and ear-muffs with earphones (loudspeakers), boom microphones, cheek-bone microphones, or throat microphones. All these solutions have one of more of the following undesirable properties:
heavy and clumsy.
uncomfortable.
inferior quality of sound pick-up and restoration.
poor noise attenuation.
attenuate both desired and unwanted sounds.
It is an object of this invention to provide an ear terminal having none of these shortcomings, being a lightweight, all-in-the-ear intelligent hearing protector with wireless communication. The noise attenuation is automatically adapted to the noise conditions and communication modes. The present invention therefore simultaneously protects the hearing and provides improved communication abilities in different noise environments. It is intended for continuous use during the working day or other periods when hearing protection and/or voice communication is needed.
The invention also concerns a device for utilising the speech sound produced in the ear of a person carrying hearing protective communications ear plugs according to the invention.
Present day devices intended to pick up speech from a person in a very noisy environment represent a technological challenge and take several forms. Common types include
A microphone in close proximity to the mouth, carried on a microphone boom. The microphone is made with a characteristic emphasising the near field from the mouth. This type is sometimes referred to as xe2x80x9cnoise cancellingxe2x80x9d,
A vibration pickup in contact with the throat, picking up the vibrations of the vocal cord.
A vibration pickup in contact with the wall of the meatus, the outer ear canal, picking up the vibrations of the tissue in the head.
A similar pickup in contact with the cheek-bone.
These device types are either fairly sensitive to acoustic noise masking the speech, or certain speech sounds are poorly transmitted, especially the high frequency consonant sounds necessary for good intelligibility.
Persons exposed to high noise levels are required by health and safety regulations to wear hearing protectors. The protectors take the form either of sealing cups which enclose the ear, or ear plugs which block the ear canal. The latter type of protector is often preferred because of its small size and relatively good comfort.
Thus it is an additional object of this invention to provide an ear plug with two desirable properties:
The cavity sealed off in the inner portion of the meatus by the ear plug is relatively free of external noise, this is the purpose of the ear plug in protecting the hearing.
The sound field in the cavity generated by the persons own voice contains all the frequency components necessary to reconstruct the speech with good intelligibility.
The solution according to invention takes advantage of these facts. By using a microphone to pick up the acoustic sound field in the inner portion of the meatus and processing the microphone signal according to the invention, a speech signal of high quality and low noise masking is produced.
It is an additional object of this invention to provide a system for increasing the user""s feeling of naturalness of the user""s own voice when using a hearing protective communications terminal according to the invention.
Using ordinary earplugs or earmuffs, the user usually feels his own voice being distorted, a feature reducing the comfort of wearing hearing protectors ordinary hearing defenders changes the normal sound transmission path from the mouth to the eardrums. Thus the auditory feedback from the users own voice is affected resulting in an unintended change in the speech output. A normal response is to raise one""s own voice level when using headsets or earplugs.
The invention solves this problem by filtering and mixing in the user""s own voice picked up by either the outer or the inner microphone at one ear and reproduce the signal at the loudspeaker in the other ear. It is also possible to reproduce the signal by the loudspeaker in the same ear, in which case feedback cancellation has to be applied. Thus the user""s voice is felt more natural both with respect to frequency response and speech level. This feature will increase the level of acceptance for continuous use of hearing protectors during the whole working day. The own voice signal is added and reproduced in such a way that the noise reduction property of the hearing protector is maintained.
An additional object of this invention is to provide a programmable personal noise exposure dose meter that measures the true exposure in the user""s ear and calculates the hearing damage risk.
Present day noise exposure dose meters, also called dosimeters, usually consist of a microphone and a small electronics unit that may be attached to the body or worn in a pocket. The microphone may be mounted on the electronics unit or it may be fastened to the collar or on the shoulder. ANSI S1.25 specifies dosimeters.
Present day dosimeters have several shortcomings:
Dosimeters do not measure the noise that actually affects the hearing organ (e.g. when the user wears a hearing protector, helmet, etc.). Even when the ear is not covered, measurements may be influenced by body shielding.
Dosimeters are susceptible to non-intentional or intentional errors, which may influence readings, such as wearers tapping or singing into dosimeter microphones or by wind-generated noise.
Dosimeters are inaccurate if impulse or impact noise is present.
The invention solves these problems by using a microphone that measures the sound at the eardrum and employs analysis procedures that take into account both stationary and impulsive sound. When the dose meter is part of a communications terminal this includes external noises, incoming communication signal, as well as possible malfunctioning of the equipment.
It is also an object of this invention to provide a device for verifying in situ that a hearing protector is properly used.
Present day hearing protectors take the form either of sealing cups which enclose the ear, or ear plugs which blocks the ear canal. For both types, it is critically important to avoid leakage of the noise sound through or around the sealing and blocking parts of the hearing protectors.
Experience shows that several factors may compromise the sealing of a hearing protector and thereby increase the risk of hearing damage. These factors include
Irregular surfaces which the sealing material is not able to follow properly. Examples are spctacles used with ear cups, and ear plugs used by persons with irregularly formed ear canals.
Improper placement of the hearing protector. Experience and patience is required by the user to get a hearing protector mounted correctly. In cases where the user is wearing a helmet or cap, the hearing protector may be accidentally pushed out of position during use.
Ageing of the materials in the sealing may reduce the resilience of the sealing and thereby allow leakage around the sealing.
The result of leakage is reduced damping of potentially harmful noise. Ideally, the leakage should be detected and remedied prior to noise exposure. The leakage may not be clearly audible. Accordingly, noise situations may comprise of intermittent or impulsive components which may damage the hearing almost instantaneously if a hearing protector should be malfunctioning or imperfect without the user""s knowledge.
The invention solves these problems by an in situ acoustical measurement, which is analysed and reported to the user in audible form, or to external equipment by means of communication signals. The devices necessary for the measurement are an integral part of the hearing protector. Verification may be activated by the user at any time, or be continuously running when the application is critical.
Optionally, verification may be activated by other persons (or devices) than the user, e.g. to verify hearing protector function before admittance to a noisy area is allowed.